Actually, I don't think that Saren is the character symbol for Synthesis. I'd say Legion is more like it. EDI may get the ending dialogue but I'd say it's more about Legion both in a symbolic and story-wise way. You see the same kind of green shown in the EC scattered throughout both Legion's loyalty mission (speaking of, the end choices in ME3 I think are also an extreme version of the choices available at the end of its ME2 mission) and in the geth consensus mission. He also represents the hope for peace among both it's people and others in said latter mission, sacrifices itself on Rannoch for peace, etc.There's also the evolution of synthetics in the story of the Mass Effect series: first game, there's hardly any good form of synthetic life; second game, Legion breaks that trend as well as the appearance of EDI; thirdly, there are many subtle moments such as the Rannoch situation, the geth consensus mission, releasing the synthesized cure on Tuchunka, your conversations with EDI, and arguments with Engineer Adams. Therefore, the Synthesis option seems like both a compromise (rather than a takeover): Shepard wants everyone to keep their physical and mental forms while the Catalyst still wants to fulfill it's job of solving the conflict that's been occuring since its creators time. Therefore, I don't think it's either a conquest or a knock on diversity but both a knock on the galaxy's prevalent belief in utilitarianism (which the Destroy and Renegade control options help to represent) and it's also a belief that a change has to be made in the galaxy via Shepard for the better (ex. Synthesis and even Paragon control).